Additive manufacturing

ABSTRACT

In one example, a non-transitory processor readable medium with instructions thereon that when executed cause an additive manufacturing machine to inhibit build material in an overlying layer of build material from fusing with a first slice formed in an underlying layer of build material.

BACKGROUND

Additive manufacturing machines produce 3D (three-dimensional) objectsby building up layers of material. Some additive manufacturing machinesare commonly referred to as “3D printers” because they often use inkjetor other printing technology to apply some of the manufacturingmaterials. 3D printers and other additive manufacturing machines make itpossible to convert a CAD (computer aided design) model or other digitalrepresentation of an object directly into the physical object.

DRAWINGS

FIGS. 1A-9A and 1B-9B present a sequence of sections and perspectivesillustrating one example for additive manufacturing an object with anunderhang.

FIGS. 10 and 11 are flow diagrams that illustrate example additivemanufacturing processes.

FIG. 12 is a block diagram illustrating one example of a processorreadable medium with instructions to help form an underhang during theadditive manufacture of an object.

FIG. 13 is a block diagram illustrating one example of an additivemanufacturing machine implementing a controller with a processorreadable medium with underhang instructions, such as the medium shown inFIG. 12.

FIG. 14 is a block diagram illustrating one example of an additivemanufacturing system implementing a CAD computer program product with aprocessor readable medium with underhang instructions, such as themedium shown in FIG. 12.

The same part numbers designate the same or similar parts throughout thefigures.

DESCRIPTION

Some additive manufacturing machines make a 3D object by coalescinglayers of powdered build material. Additive manufacturing machines makeobjects based on data in a 3D model created, for example, with a CADcomputer program product. The model data is processed into slices, eachdefining that part of a layer or layers of build material to becoalesced. The examples of additive manufacturing described below use atechnique in which a light absorbing ink or other suitable coalescingagent is “printed” on to a layer of build material in the desiredpattern and then exposed to light to coalesce the patterned buildmaterial. Coalescing agents increase light absorption to generatesufficient heat to sinter, melt or otherwise coalesce the patternedbuild material for solidification directly (as in sintering) orindirectly through cooling (as in melting).

Coalescing agent may bleed into build material outside the desiredpattern, causing the unwanted coalescence and solidification of buildmaterial. Also, heat generated in the patterned build material can,under some circumstances, propagate into and solidify surrounding,unpatterned build material. The unwanted solidification of buildmaterial can degrade the overall dimensional accuracy and appearance ofthe manufactured object. Such degradation is often manifested, forexample, in poorly defined edges. Modifier agents have been developed toblock or neutralize the effects of a coalescing agent. The unwantedsolidification of build material may be controlled by dispensing acoalescence modifier agent on to unpatterned build material surroundingbuild material patterned with a coalescing agent. For example, modifieragents and additive manufacturing processes are described ininternational patent application no. PCT/US2014/036169 filed Apr. 30,2014, titled Three Dimensional Printing Method, to prevent or reduce thedegree of coalescence of targeted areas of build material to helpcontrol dimensional accuracy and surface roughness along the edges ineach layer of the manufactured object.

It has been discovered that coalescence modifier agents may also be usedto control unwanted fusing between build material and object slices,fusing that can lead to excessive surface roughness in objects with anunderhang (that part of an underlying slice that extends past anoverlying slice). Accordingly, a new additive manufacturing process hasbeen developed to inhibit or prevent interlayer fusing to obtain smooth,well defined underhangs.

In one example, the new process includes applying a coalescence modifieragent on to a first object slice formed in a first layer of buildmaterial as a fusion barrier to protect the top surface of the firstslice during formation of a second slice. The modifier agent is appliedat locations bordering the area where the second slice will cover thefirst slice, covering at least part of the underhang. Then, when buildmaterial in a second, overlying layer is heated to form the secondslice, the fusion barrier prevents, or at least inhibits, heated buildmaterial in the second layer from fusing with the first slice in theunderhang area so that the top of the underhang on the second slice willremain smooth and well defined. A processor readable medium withinstructions for underhang surface control using a coalescence modifieragent may be implemented, for example, in a CAD computer programproduct, in an object model processor, or in the controller for theadditive manufacturing machine.

As used in this document: a “coalescing agent” means a substance thatcauses or helps cause a build material to coalesce; a “coalescencemodifier agent” means a substance that inhibits or prevents coalescenceof a build material including, for example, modifying the effect of acoalescing agent; a “slice” means a slice of a multi-slice object; andan “underhang” means that part of an underlying slice that extends pastan overlying slice (i.e., an upside down overhang).

The sequence of sections and perspectives presented in FIGS. 1A-9A and1B-9B illustrate one example for additive manufacturing an object withan underhang. FIG. 10 is a flow diagram illustrating one example of anadditive manufacturing process 100 implemented in FIGS. 1A-9A, 1B-9B.Referring to FIGS. 1A-9A, 1B-9B and FIG. 10, a first layer 12 of buildmaterial 14 is formed, as shown in FIGS. 1A, 1B (block 102 in FIG. 10).A coalescing agent 16 is dispensed on to build material 14, as shown inFIGS. 2A, 2B, in a pattern 20 corresponding to an object slice, forexample with an inkjet type dispenser 18 (block 104 in FIG. 13).Coalescing agent pattern 20 is depicted by dense stippling in thefigures. Any suitable build material 14 may be used to make object 10,shown in FIGS. 9A and 9B, which may be hard or soft, rigid or flexible,elastic or inelastic. Also, while a powdered build material 14 isdepicted by particles 22 in this example, suitable non-powdered buildmaterials could also be used.

In FIGS. 3A, 3B, the area 20 of layer 12 patterned with coalescing agentis exposed to light 24 from a light source 26 to coalesce build materialand, upon solidification, form a first object slice 28 (block 106 inFIG. 10). Depending on the characteristics of build material 14,coalescing agent 16 and light 24, the build material may coalesce, forexample, by melting to a liquid or by sintering to a solid. If the buildmaterial melts, then solidification occurs upon cooling.

In FIGS. 4A, 4B, a coalescence modifier agent 30 is dispensed on toslice 28 in a pattern 32 covering an area 34 where a second object slicewill underhang the first slice (block 108 in FIG. 10), for example withan inkjet type dispenser 36. Modifier agent pattern 32 is depicted bysparse stippling in the figures. In the example shown, the pattern 32for modifier agent 30 is co-extensive with underhang area 34. Otherunderhang patterns 32 are possible. For example, if light source 26 isconfigured to selectively illuminate only those portions of buildmaterial patterned with coalescing agent, then it may be desirable tolimit pattern 32 to locations immediately bordering the second slicepattern in the underhang areas. (Second slice pattern 44 is shown inFIGS. 7A, 7B.) If, however, light source 26 is configured to illuminatemost or all of each layer of build material, then it usually will bedesirable for modifier agent pattern 32 to completely cover underhangarea 34 as shown in FIGS. 4A and 4B.

Coalescence modifier agent 30 may also be dispensed on to other areas ofbuild material in each layer to help define other aspects of the objectslices including, for example, interspersed with the pattern of thecoalescing agent to change the material characteristics of the slice.Although two distinct dispensers 18, 36 are shown, agents 16 and 30could be dispensed from the same dispensers integrated into a singledevice, for example using different printheads (or groups of printheads)in a single inkjet printhead assembly.

For a liquid modifier agent 30, it may be desirable to dry the patternedarea 32 before forming the next layer of build material. In the exampleshown in FIGS. 5A, 5B, the area of slice 28 patterned with modifieragent is heated to dry the modifier agent and form a solid fusionbarrier 38. In other examples, it may be desirable to allow a liquidmodifier agent 30 to dry without added heating. Heater 40 in FIG. 5Arepresents generally any suitable heater, which may include one or moreof thermal radiation, convection and conduction.

In FIGS. 6A, 6B, a second layer 42 of build material 14 is formed overfirst layer 12 covering first slice 28 (block 110 in FIG. 10). In FIGS.7A, 7B, a coalescing agent 16 is dispensed on to build material 14 inlayer 42 in a pattern 44 corresponding to a second object sliceunderhanging first slice 28 (block 112 in FIG. 10). In FIGS. 8A, 8B,area 44 patterned with coalescing agent is exposed to light 24 tocoalesce build material and, upon solidification, form a second objectslice 46 (block 114 in FIG. 10). While distinct first and second slices28, 46 are shown in FIGS. 8A, 8B, the two slices actually fuse togetherinto a single part. The now fused slices 28, 46 are separated from thebuild material and the fusion barrier, in a process sometimes referredto as “uncaking”, as a finished object 10 shown in FIGS. 9A and 9B.Second slice 46 includes part 48 that underhangs first slice 46. While asimple two-slice object 10 is shown, the same process steps may be usedto form more complex, multi-slice objects.

FIG. 11 is a flow diagram illustrating another example of an additivemanufacturing process 120. Referring to FIG. 11, a first layer of buildmaterial is formed (block 122) and build material in the first layersolidified to form a first slice (block 124), for example as describedabove with reference to FIGS. 1A-3A, 1B-3B. A coalescence modifier agentis dispensed on to the first slice covering an area where the firstslice will underhang the second slice (block 126), for example asdescribed above with reference to FIGS. 4A and 4B. A second layer ofbuild material is formed on the first layer of build material (block128) and build material in the second layer is solidified to form asecond slice on the first slice (block 130), for example as describedabove with reference to FIGS. 6A-8A, 6B-8B. If a liquid coalescencemodifier agent is used, the modifier agent may be dried before formingthe second layer of build material, for example by actively heating themodifier agent as shown in FIGS. 5A and 5B. In another example, the heatin a newly formed slice may be sufficient to dry the liquid modifieragent without additional heating.

FIG. 12 is a block diagram illustrating a processor readable medium 50with instructions 52 to help form an underhang during the manufacture ofa 3D object. A processor readable medium 50 is any non-transitorytangible medium that can embody, contain, store, or maintaininstructions for use by a processor. Processor readable media include,for example, electronic, magnetic, optical, electromagnetic, orsemiconductor media. More specific examples of suitable processorreadable media include a hard drive, a random access memory (RAM), aread-only memory (ROM), memory cards and sticks and other portablestorage devices.

Underhang instructions 52 include instructions to inhibit build materialin an overlying layer of build material from fusing with a first sliceformed in an underlying layer of build material, for example bydispensing a coalescing modifier agent at block 126 in FIG. 11.Instructions 52 may include other additive manufacturing instructions,for example instructions to form and solidify shown at blocks 122, 124,128 and 130 in FIG. 11. Processor readable medium 50 with instructions52 may be implemented, for example, in a CAD computer program product,in an object model processor, or in a controller for an additivemanufacturing machine. Control data to inhibit fusing can be generated,for example, by processor readable instructions on the sourceapplication, usually a CAD computer program product, in an object modelprocessor, or by processor readable instructions on the additivemanufacturing machine.

FIG. 13 is a block diagram illustrating one example of an additivemanufacturing machine 54 implementing a controller 56 with overhanginstructions 52. Referring to FIG. 13, machine 54 includes controller56, a manufacturing bed or other suitable support 58, a roller or othersuitable build material layering device 60, a coalescing agent dispenser18, a coalescence modifier agent dispenser 36, a heater 40 and a lightsource 26. The in-process object structure is supported on support 58during manufacturing. In some machines 54, support 58 may be movable atthe urging of controller 56 to compensate for the changing thickness ofthe in-process structure, for example as layers of build material areadded during manufacturing.

Build material layering device 60 layers build material on support 58and on the in-process structures and may include, for example, a deviceto dispense the build material and a blade or roller to distribute thebuild material uniformly to the desired thickness for each layer.Coalescing agent dispenser 18 dispenses coalescing agent selectively atthe direction of controller 56 on to build material, for example asdescribed above with reference to FIGS. 2A and 7A. Coalescence modifieragent dispenser 36 dispenses modifier agent selectively at the directionof controller 56 on to build material, for example as described abovewith reference to FIG. 4A. While any suitable dispensers 18, 36 may beused, inkjet printheads are often used in additive manufacturingmachines because of the precision with which they can dispense agentsand their flexibility to dispense different types and formulations ofagents. Manufacturing machine 54 may include a heater 40 if it isdesired to pre-heat build material or to heat modifier agent. Lightsource 26 applies light 24 selectively at the direction of controller 56to coalesce build material treated with coalescing agent, for example asdescribed above with reference to FIGS. 3A and 8A.

Controller 56 represents the processor (or multiple processors), theassociated memory (or multiple memories) and instructions, and theelectronic circuitry and components needed to control the operativeelements of machine 54. In particular, controller 56 includes a memory62 having a processor readable medium 50 with underhang instructions 52,and a processor 64 to read and execute instructions 52. For example,controller 56 would receive control data and other instructions from aCAD program to make an object that includes an overhang and executelocal underhang instructions 52 as part of the process of making theobject.

Alternatively, underhang instructions 52 may be embodied in a processorreadable medium 50 separate from controller 56, for example as part of aCAD computer program product shown in FIG. 14. Referring to FIG. 14, anadditive manufacturing system 66 includes an additive manufacturingmachine 54 operatively connected to a CAD computer program product 68with underhang instructions 52 residing on a processor readable medium50. Any suitable connection between machine 54 and CAD program product68 may be used to communicate instructions and control data to machine54 including, for example, a wired link, a wireless link, and a portableconnection such as a flash drive or compact disk.

Light source 26 applies light energy to build material to cause thecoalescence of portions of the build material according to wherecoalescing agent has been delivered or has penetrated. In some examples,light source 26 is an infra-red (IR) or near infra-red light source, ora halogen light source. Light source 26 may be a single light source oran array of multiple light sources. In some examples, light source 26 isconfigured to apply light energy in a substantially uniform mannersimultaneously to the whole surface of a layer of build material. Inother examples, light source 26 is configured to apply energy to onlyselect areas of the whole surface of a layer of build material.

Build material may be a powder, a liquid, a paste, or a gel. Examples ofbuild material include semi-crystalline thermoplastic materials with aprocessing window of greater than 5° C. (i.e., the temperature rangebetween the melting point and the re-crystallization temperature).Suitable build materials may include polyamides (e.g., PA or nylon 11,PA or nylon 12, PA or nylon 6, PA or nylon 8, PA or nylon 9, PA or nylon66, PA or nylon 612, PA or nylon 812, PA or nylon 912), polyethylene,polyethylene terephthalate (PET), polystyrene, polyacetals,polypropylene, polycarbonate, polyester, thermal polyurethanes, otherengineering plastics, and blends of any two or more of the polymerslisted. Core shell polymer particles of these materials may also beused.

Build material may have a melting point ranging from about 50° C. toabout 400° C. In some implementations, it is desirable that the meltingpoint of the build material be less than (lower than) the melting pointof an inorganic salt used in the modifier agent. As examples, polyamide12 having a melting point of 180° may be used, or thermal polyurethaneshaving a melting point ranging from about 100° C. to about 165° C. maybe used. In one example, when a combination of polymer particles is usedin the build material, at least one of the particles has a melting pointbelow the melting point of the inorganic salt in the modifier agent.

The build material may be made up of similarly sized particles ordifferently sized particles. In the example shown in the figures, thebuild material includes particles of three different sizes. As oneexample of the different sizes for each of the build material particles,the average of each size particle may be greater than 50 μm, between 10μm and 30 μm, and less than 10 μm. In an example, the largest particlesare present in an amount ranging from 70 wt % to 95 wt %, the mediumparticles present in an amount ranging from 0.5 wt % to 21 wt %, and thesmallest particles present in an amount ranging from greater than 0 wt %up to 21 wt %.

Build material may include, in addition to polymer particles, a chargingagent and a flow aid. A charging agent may be added to suppresstribo-charging. Suitable charging agents may include aliphatic amines(which may be ethoxylated), aliphatic amides, quaternary ammonium salts(e.g., behentrimonium chloride or cocamidopropyl betaine), esters ofphosphoric acid, polyethylene glycol esters, or polyols. Some suitablecommercially available charging agents include HOSTASTAT® FA 38 (naturalbased ethoxylated alkylamine), HOSTASTAT® FE2 (fatty acid ester), andHOSTASTAT® HS 1 (alkane sulfonate), each of which is available fromClariant Int. Ltd.). In an example, the charging agent is added in anamount ranging from greater than 0 wt % to less than 5 wt % based uponthe total wt % of the polymer particles. A flow aid improves theflowability of build material by reducing friction, lateral drag, andtribo-charging, and may be particularly desirable when build materialparticles are less than 25 μm in size. Examples of suitable flow aidsinclude tricalcium phosphate (E341), powdered cellulose (E460(ii)),magnesium stearate (E470b), sodium bicarbonate (E500), sodiumferrocyanide (E535), potassium ferrocyanide (E536), calcium ferrocyanide(E538), bone phosphate (E542), sodium silicate (E550), silicon dioxide(E551), calcium silicate (E552), magnesium trisilicate (E553a), talcumpowder (E553b), sodium aluminosilicate (E554), potassium aluminiumsilicate (E555), calcium aluminosilicate (E556), bentonite (E558),aluminium silicate (E559), stearic acid (E570), or polydimethylsiloxane(E900). In an example, the flow aid is added in an amount ranging fromgreater than 0 wt % to less than 5 wt % based upon the total wt % of theparticles.

Suitable coalescing agents include water-based dispersions with anactive, radiation absorbing binding agent. The active agent may be, forexample, an infrared light absorber, a near infrared light absorber, ora visible light absorber. As one example, the coalescing agent may be anink-type formulation including carbon black as the active material. Anexample of this ink-type formulation is commercially known as CM997Aavailable from Hewlett-Packard Company. Examples of inks includingvisible light enhancers as the active agent are dye based colored inkand pigment based colored ink. Examples of pigment based inks includethe commercially available inks CM993A and CE042A, available fromHewlett-Packard Company. The aqueous nature of some coalescing agentenables the coalescing agent to penetrate the layer of build material.For hydrophobic build materials the presence of a co-solvent and/or asurfactant in the coalescing agent may assist in obtaining the desiredwetting. One or more coalescing agents may be dispensed to form eachslice.

Suitable coalescence modifier agents may separate individual particlesof the build material to prevent the particles from coalescing. Examplesof this type of modifier agent include colloidal, dye-based, andpolymer-based inks, as well as solid particles that have an average sizeless than the average size of particles of the build material. Themolecular mass of the modifier agent and its surface tension may be suchthat it enables the agent to penetrate sufficiently into the buildmaterial to achieve the desired mechanical separation. In one example, asalt solution may be used as a coalescence modifier agent. In otherexamples, inks commercially known as CM996A and CN673A available fromHewlett-Packard Company may be used as a coalescence modifier agent.

Suitable coalescence modifier agents may act to modify the effects of acoalescing agent by preventing build material from reaching the meltingpoint. A fluid that exhibits a suitable cooling effect may be used asthis type of coalescence modifier agent. For example, when buildmaterial is treated with a cooling fluid, energy applied to the buildmaterial may be absorbed evaporating the fluid to help prevent buildmaterial from reaching its melting point. Thus, for example, a fluidwith a high water content may be a suitable coalescence modifier agent.

“A” and “an” used in the claims means one or more.

The examples shown in the figures and described above illustrate but donot limit the scope of the patent, which is defined in the followingClaims.

1-4. (canceled)
 5. A non-transitory processor readable medium havinginstructions thereon that when executed cause an additive manufacturingmachine to form a physical barrier on an underlying object slice tooverlying build material fusing with the underlying object slice. 6-7.(canceled)
 8. The medium of claim 5, where the instructions to form aphysical barrier include instructions to dispense a liquid coalescencemodifier agent on to the underlying object slice bordering an area wherean overlying object slice in the overlying build material will cover theunderlying object slice.
 9. A computer program product that includes theprocessor readable medium of claim
 5. 10. An additive manufacturingmachine controller that includes the processor readable medium of claim5. 11-14. (canceled)
 15. The medium of claim 5, where the instructionsto form a physical barrier include instructions to dry the modifieragent dispensed on to the underlying object slice before forming theoverlying build material.
 16. An additive manufacturing machine,comprising: an apparatus for form slices of an object; and a controllerhaving instructions thereon that when executed: cause the apparatus toform an underlying object slice; cause the apparatus to form a physicalbarrier on the underlying object slice to overlying build materialfusing with the underlying object slice; and cause the apparatus to, inthe overlying build material, form an overlying object slice on theunderlying object slice.
 17. The machine of claim 16, wherein: theapparatus comprises: a first device to layer powdered build material; asecond device to dispense a liquid, light absorbing coalescing agent onto build material; a third device to dispense a liquid coalescencemodifier agent on to build material; a light source to apply lightenergy to build material; the instructions to cause the apparatus toform the underlying object slice include instructions to: cause thefirst device to layer build material in a first layer; cause the seconddevice to dispense a liquid, light absorbing coalescing agent on tobuild material in the first layer in a first pattern of the underlyingobject slice; and cause the light source to apply light energy to buildmaterial in the first layer patterned with coalescing agent to generateheat to melt patterned build material in the first layer, to form theunderlying object slice; the instructions to cause the apparatus to formthe physical barrier include instructions to cause the third device todispense a liquid coalescence modifier agent on to the underlying objectslice bordering an area where the overlying object slice will cover theunderlying object slice; and the instructions to cause the apparatus toform the overlying object slice include instructions to: cause the firstdevice to layer build material in a second layer over the underlyingobject slice; cause the second device to dispense a liquid, lightabsorbing coalescing agent on to build material in the second layer in asecond pattern of the overlying object slice; and cause the light sourceto apply light energy to build material in the second layer patternedwith coalescing agent to generate heat to melt patterned build materialin the second layer, to form the overlying object slice on theunderlying object slice.
 18. The machine of claim 17, wherein theinstructions to cause the apparatus form the barrier includeinstructions to dry the modifier agent dispensed on to the underlyingobject slice before layering build material over the underlying objectslice.
 19. A non-transitory processor readable medium havinginstructions thereon that when executed cause an additive manufacturingmachine to: form a first layer of build material; dispense a liquid,light absorbing coalescing agent on to build material in the first layerin a pattern of a first slice of an object; expose build material in thefirst layer patterned with coalescing agent to light to generate heat tomelt patterned build material in the first layer to form the firstslice; dispense a liquid coalescence modifier agent on to the firstslice covering an area where the first slice will underhang a secondslice of the object; form a second layer of build material on the firstslice; dispense a liquid, light absorbing coalescing agent on to buildmaterial in the second layer in a pattern of the second slice; andexpose build material in the second layer patterned with coalescingagent to light to generate heat to melt patterned build material in thesecond layer to form the second slice on the first slice.
 20. The mediumof claim 19, having instructions to dry the modifier agent on the firstslice before forming the second layer of build material.
 21. The mediumof claim 20, wherein the instructions to dry the modifier agent includeinstructions to heat the modifier agent.